Hello Gerd, Here is more information about how I obtained my result. I used mkgmap v4107 and splitter v590. My options for DEM are : dem=./MySrtm1Folder dem-dists=3312,13248,26512,53024,106048 dem-poly=./MyPolygon.poly dem-interpolation=auto overview-dem-dist=212096 I do not define any polygon option for splitter. As explained in my previous email, to avoid the generation of a shadow in plain ocean, I defined a new polygon inside the correct shadow rendering area and it solved my problem. For the artifacts I described, follow this link to see what I mean : http://emerald-island.eu/wikka/ShadowArtifacts It was made with mkgmap version 41067 and 4126 and splitter 590 with the same result. Again for your great work, chapeau bas, David